Stand characteristics and dynamics of sub-spontaneous European yew (Taxus baccata L.) in a Central European urban forest (Potsdam-Telegrafenberg)

Abstract In northern Central Europe, larger sub-spontaneous occurrences of the European yew developed in the 20th/twenty-first century in the vicinity of settlements. Using the example of such an occurrence on the Telegrafenberg hill at Potsdam, the population characteristics and dynamics of the yew as well as the local forest vegetation and site characteristics were investigated. For this purpose methods from population ecology, geobotany, dendrochronology, and soil science were applied. Starting from yews planted as ornamental trees at the end of the nineteenth century, a population of 2341 specimens has developed over an area of 27 ha, largely characterised by sub-spontaneous individuals. Trees with a height up to 1 m predominate. The maximum tree height is 11 m. Whereas the oldest specimen is 116 years old (AD 1909), most yews are only a few decades old, as the root collar diameters demonstrate. The tree-ring site chronology developed for 14 yew trees indicates a strong common growth signal. Local tree growth seems to profit to some extent from high temperatures in late winter to spring, but mainly from precipitation in late spring to summer and suffers, but not lethally, from high temperatures in summer. The sub-spontaneous yews are part of older sessile oak stands, which previously also included Scots pine disappearing recently due to drought-related dieback. These stands are characterised by a dense shrub layer, consisting of yews and mainly Norway and sycamore maple, black cherry and others. The soils are sandy podzolised Cambisols (Dystric Arenosols) with moder humus. Both forest vegetation and soil properties indicate a poor to medium nutrient supply and a medium dry soil water regime at Telegrafenberg. This local example underlines the potential of yew as a relatively drought-resistant species, offering a forest tree that is well adapted to an increasingly warm and dry regional climate. In general, sub-spontaneous yew occurrences complement well autochthonous stands of this endangered and protected tree species in the wider region.